1

Supplementary Information

First identification of unstable phosphino formic

acid (H2PCOOH)

Cheng Zhu,a Robert Frigge,a Andrew M. Turner,a Ralf I. Kaiser,*a Bing-Jian Sun,b

Si-Ying Chenb and Agnes H.H. Changb

aDepartment of Chemistry, University of Hawaii at Mānoa, Honolulu, HI 96822

W.M. Keck Laboratory in Astrochemistry, University of Hawaii at Mānoa, Honolulu, HI 96822

bDepartment of Chemistry, National Dong Hwa University, Shoufeng, Hualien 974, Taiwan

.

Corresponding Author

*E-mail: ralfk@hawaii.edu

Content:Materials & Methods – Experimental Materials & Methods – TheoreticalFig. S1Table S1 to S5

Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2018

2

Materials & Methods – Experimental

The experiments were conducted in a contamination-free ultrahigh vacuum chamber with a

base pressure 8 × 1011 Torr, which was rendered using a magnetically suspended turbo

molecular pump (Osaka TG420 MCAB) backed by an oil-free scroll pump (Anest Iwata ISP-

500).1 Within the chamber, a silver mirror substrate is interfaced to a cold head (Sumitomo

Heavy Industries, RDK-415E), which is connected to a closed cycle helium compressor capable

of reaching 5.0 ± 0.1 K. By utilizing a doubly differentially pumped rotational feedthrough

(Thermionics Vacuum Products, RNN-600/FA/ MCO) the substrate is able to be rotated in the

horizontal plane; utilizing an UHV compatible bellow (McAllister, BLT106) the substrate can be

translated in the vertical plane as well. The gas mixture was prepared in a gas mixing chamber by

the sequential addition of 10 mbar of phosphine (PH3, Sigma-Aldrich, 99.9995%;) and 100 mbar

of carbon dioxide (CO2, Airgas, 99.999%;13CO2, Aldrich, 99% 13C; C18O2, Aldrich, 95% 18O).

The premixed gases were then deposited to the silver wafer at 5 K via a precision leak value and

glass capillary array for 15 min at a pressure of 2 × 10 Torr in the main chamber. The thickness

of the ice was determined in situ via laser interferometry with one helium-neon (He-Ne) laser

operating at 632.8 nm.2 The light from the laser was reflected at angles of 4° relative to the ice

surface normal. Considering the ratio of phosphine (PH3) and carbon dioxide (CO2) (1:10; see

below) and the refractive indexes of pure phosphine (PH3, nPH3 = 1.51 ± 0.04) and carbon

dioxide (nCO2 = 1.27 ± 0.02) ices 2, 3, the ice thickness was determined to 830 ± 50 nm.

The deposited ice was then monitored via a Fourier Transform Infrared (FTIR) spectrometer

(Nicolet 6700) from 6,000–500 cm−1 and a resolution of 4 cm−1. Fig. S1(a) depicts the IR

spectrum of phosphine (PH3) and carbon dioxide (CO2) ice. Vibrational assignments were

compiled in Table S1. Based on the integrated areas along with absorption coefficients of 1.40 ×

1018 cm molecule, 4.50 × 10 cm molecule1, 7.80 × 1017 cm molecule1，7.1× 1019 cm

molecule, and 5.1 × 1019 cm molecule for the 3699 cm1 (ν1 + ν3, CO2), 3594 cm1 (2ν2 + ν3,

CO2), 2274 cm1 (ν3, 13CO2), 1103 cm1 (ν4, PH3), and 987 cm1 (ν2, PH3) bands, respectively,

the relative abundance of phosphine (PH3) and carbon dioxide (CO2) was determined to be

nominally 1:10,2, 3 which matches the gas phase ratio. Furthermore, the absorptions of carbon

dioxide (CO2) at 3699 cm1 (ν1 + ν3) and 3594 cm1 (2ν2 + ν3) are red shifted from that of pure

carbon dioxide (CO2) ice (Fig. S1(b)), which probably due to the complexation effect of carbon

3

dioxide (CO2) and phosphine (PH3), e.g., redistribution of the partial atomic charges and change

of the bond orders.

The ices were then isothermally irradiated at 5.0 ± 0.1 K with 5 keV electrons from a Specs

EQ 22-35 electron gun at nominal beam current of 0 nA (blank), 100 nA. The electrons were

introduced at an angle of 70° relative to the target surface and expanded to cover the ice area (1.0

± 0.1 cm). Monte Carlo simulations (Casino 2.42)4 were exploited to model the electron

trajectories and energy transfer inside the ices. Considering the densities of phosphine (PH3, 0.90

g cm−3)2 and carbon dioxide (CO2, 1.11 g cm−3),3 the average and maximum penetration depths

of the 5 keV electrons were calculated to be 300 ± 40 and 700 ± 80 nm, respectively, which are

less than the thickness of the deposited ice mixtures of 830 ± 50 nm ensuring negligible

interaction between the substrate and the electrons. The averaged dose was calculated to be 2.8 ±

0.6 per molecule. During the irradiation, IR spectra of the ices were continuously measured

every 2 minutes. New absorptions at 2284 cm1 (P2H4),2 2137 cm1 (CO, 2137 cm1),3 and 2092

cm1 (13CO)3 were identified in the IR spectrum of the 100 nA irradiated phosphine (PH3) and

carbon dioxide (CO2) ice. The most intense absorptions of phosphino formic acid (H2PCOOH),

e.g., 1101, 1131, and 1790 cm1, were not found in the spectrum since FTIR is relatively

insensitive compared to PI-ReTOF-MS by at least four orders of magnitude,5 and the present low

dose experiment was designed to initiate only the initial reactions in the carbon dioxide –

phosphine ices and hence to exclude the formation of higher phosphanes.

After the irradiation, the ices were heated at a rate of 1 K min1 to 320 K while any subliming

molecules were detected using a reflectron time-of-flight (ReTOF) mass spectrometer (Jordon

TOF Products, Inc.) with single photon ionization.1 This photoionization process utilizes

difference four wave mixing to produce vacuum ultraviolet light (ωvuv = 2ω1 – ω2). The

experiments were performed with 10.86 eV photoionization energy and repeated at 9.60 eV to

distinguish between the isomers of the phosphino formic acid (H2PCOOH). To produce 10.86

eV, the second harmonic (532 nm) of a pulsed neodymium-doped yttrium aluminum garnet laser

(Nd:YAG, Spectra Physics, PRO-270, 30 Hz) was used to pump a Rhodamine 610/640 dye

mixture (0.17/0.04 g L1 ethanol) to obtain 606.9 nm (2.04 eV) (Sirah, Cobra-Stretch), which

underwent a frequency tripling process to achieve ω1 = 202.3 nm (6.13 eV) (β-BaB2O4 (BBO)

crystals, 44° and 77°). A second Nd:YAG laser pumped an LDS 867 (0.15 g L−1 ethanol) dye to

obtain ω2 = 890 nm (1.39 eV), which when combined with 2ω1, using krypton as a non-linear

4

medium, generated ωvuv = 114.2 nm (10.86 eV) at 1014 photons per pulse. The production of 9.60

eV occurred similarly except the third harmonic (355 nm) of the second Nd:YAG laser was used

to pump a Coumarin 480 (0.40 g L−1 ethanol) dye to obtain ω2 = 472.1 nm (2.63 eV). The VUV

light was spatially separated from other wavelengths (due to multiple resonant and non-resonant

processes (2ω1 + ω2; 2ω1 ω2; 3ω1; 3ω2)) using a lithium fluoride (LiF) biconvex lens (ISP

Optics) and directed 2 mm above the sample to ionize subliming molecules. The ionized

molecules were mass analyzed with the ReTOF mass spectrometer where the arrival time to a

multichannel plate is based on mass-to-charge ratios, and the signal was amplified with a fast

preamplifier (Ortec 9305) and recorded with a personal computer multichannel scalar (FAST

ComTec, P7888-1 E), which is triggered via the pulse delay generator at 30 Hz. Here the ReTOF

signal is the average of 3600 sweeps of the mass spectrum in 4 ns bin widths, which corresponds

to an increase in the substrate temperature of 2 K between the ReTOF data points.

Materials and Methods – Theoretical

The geometries of phosphino formic acid (H2PCOOH) and carbamic acid (H2NCOOH)

isomers are optimized by the hybrid density functional B3LYP6-9 with the cc-pVTZ basis set and

the harmonic frequencies obtained (Tables S2 and S3). The corresponding coupled cluster10-13

CCSD(T)/cc-pVDZ, CCSD(T)/ccpVTZ, and CCSD(T)/cc-pVQZ energies are calculated and

extrapolated to completed basis set limits,14 CCSD(T)/CBS, with B3LYP/cc-pVTZ zero-point

energy corrections. Likewise, the species along the phosphino formic acid (H2PCOOH) and

carbamic acid (H2NCOOH) decomposition pathways are predicted at the same level of theory

(Tables S4 and S5). The energies are expected to be accurate within 0.08 eV.15 The adiabatic

ionization energies are computed by taking the energy difference between the neutral and ionic

species that correspond to similar conformation. The adiabatic ionization energies at this level of

calculations (B3LYP/cc-pVTZ//CCSD(T)/CBS) are expected to be accurate within 0.05 eV.16

The GAUSSIAN09 program17 was utilized in the electronic structure calculations.

5

Fig. S1. (a) Infrared spectrum of phosphine (PH3)carbon dioxide (CO2) ice. The absorption

features in the range of 2500 2290 cm1 are deconvoluted with Gaussian functions (dash lines).

(b) Infrared spectra in the range of 3800 3500 cm1 of phosphine (PH3)carbon dioxide ice

(CO2) (red) and pure carbon dioxide (CO2) ice (black).

6

Table S1. Absorption peaks observed in pristine phosphine (PH3) – carbon dioxide (CO2) ice.

Assignment Wavenumber (cm1)CO2 (ν2) 6653

PH3 (ν2) 9872

PH3 (ν4) 11032

13CO2 (ν3) 22743

PH3(ν1/ν3) 23262

CO2 (ν3) 2372-23333

PH3(ν1 + ν3) 24232

PH3 (ν1 + ν4) 34102

CO2 (2ν2 + ν3) 35873

CO2 (ν1 + ν3) 36953

7

Table S2: Computed Cartesian coordinates (Å), vibrational frequencies (cm1), and IR

intensities (km mol1) for various isomers of phosphino formic acid (H2PCOOH).

Cartesian coordinateaName and formula # Structure

Atom X Y ZVibrational frequency

IR intensities

P 1.339853 -0.040703 -0.118564

H 1.607026 1.018713 0.780168

H 1.476858 -1.072409 0.842620

C -0.520039 0.131164 0.012837

O -1.114431 1.174103 0.006292

O -1.132180 -1.075951 0.005224

1a

H -2.088548 -0.907952 -0.013483

157.69297.6187427.3112492.8792655.8341695.2596826.3971851.39291101.94741130.96821315.98391790.10922414.01722429.8493701.5389

4.29262.30659.146

27.2694106.597752.54944.73143.0997

136.1168166.354423.2594323.344930.253435.781852.6963

P -1.326274 0.022015 -0.119931

H -1.583164 -0.964407 0.859802

H -1.475066 1.115659 0.777315

C 0.551832 -0.136740 0.012026

O 1.100186 -1.197174 0.006242

O 1.269042 1.016464 -0.000045

Phosphino formic acid

(H2PCOOH)

1b

H 0.687523 1.784648 0.040118

128.0346306.4442410.3684441.1907566.6445716.9487815.6209841.74351098.29471131.82981268.30741828.98192370.19962435.28553795.251

6.63718.028324.741166.54053.910719.813331.34297.202183.00827.9451386.2515289.683755.627523.921844.5835

P -0.081604 -1.359646 0.000000

H 1.334325 -1.520806 0.000000

326.3528357.7777480.8702519.8393540.3575613.6505

6.988822.35772.921658.9443123.65283.6127

8

C 0.000000 0.367115 0.000000

O -1.085390 1.150562 0.000000

H -1.876529 0.598580 0.000000

O 1.073212 1.162293 0.000000

2a

H 1.863677 0.611391 0.000000

753.6866916.47211141.90271169.10211408.25231446.0812346.23913795.96233815.2421

5.87341.224470.6278359.115651.5304549.849193.543986.573368.5687

P -0.198350 -1.373419 0.000000

H 1.213010 -1.594405 0.000000

C 0.000000 0.336801 0.000000

O -1.062194 1.148317 0.000000

H -0.757156 2.065852 0.000000

O 1.140472 1.058336 0.000000

2b

H 1.893179 0.455804 0.000000

293.5013358.3573476.4882479.6489527.8369605.5234740.6149937.34381106.82691184.66921364.60151477.82332325.65453761.69173800.7153

126.02072.099513.96188.302665.90940.573817.765963.9698276.2262175.9576152.4949347.4136113.8864126.607465.2495

P -0.020432 -1.382416 0.000000

H -1.437673 -1.454663 0.000000

C 0.000000 0.335539 0.000000

O 1.139462 1.064353 0.000000

H 1.903361 0.474547 0.000000

O -1.064137 1.140941 0.000000

Enol tautomer

(HPC(OH)2)

2c

H -0.761801 2.060774 0.000000

318.5421346.9201451.7892476.7941536.4282611.3931741.8152884.31311107.23071191.43771363.69521484.65372394.6033737.47993786.4297

176.66476.09756.274

15.522537.25852.212914.253229.8335270.8496188.0745141.0895350.274149.3774100.516171.8439

9

P 1.388121 -0.099688 0.009688

H 1.550885 1.307770 -0.114864

C -0.313362 0.004870 -0.002833

O -1.062761 -1.126646 -0.068450

H -1.834621 -1.044616 0.508800

O -1.035528 1.148497 0.055324

2d

H -1.871596 1.028144 -0.417238

270.8385352.8225461.276474.6655532.5159571.4574738.5969905.47521106.57611198.39381266.26071463.0632377.91883724.14313734.3953

152.845913.2484166.691110.35956.504712.22610.041651.4839308.5157.5758

299.9969123.686964.279733.901361.083

P 1.357968 -0.164726 0.000000

H 0.943571 -1.065508 1.021791

H 0.943571 -1.065508 -1.021791

O 0.000000 0.871204 0.000000

O -1.586940 -0.751361 0.000000

C -1.266294 0.399399 0.000000

3a

H -1.963379 1.246760 0.000000

153.9445225.2565275.55

662.8877736.4491910.5112959.72931041.21821117.52511130.92631386.33661803.4612361.87862369.16113032.038

6.436810.825817.459357.87513.572214.861985.12750.003

110.1822259.15144.1213

250.190142.640874.514349.0674

P -1.257685 -0.257608 -0.116436

H -1.130218 -0.887665 1.153461

H -2.205493 0.686580 0.361569

O 0.033907 0.879044 0.037089 3b

O 1.536103 -0.798069 -0.009759

164.413189.9799298.3938643.5047749.7565923.3642954.20591037.08311115.72151194.68841382.03171782.8488

1.999211.052919.814141.374519.301843.531624.96181.346629.4086295.69683.4002

264.5268

10

C 1.271790 0.372332 0.002601

H 2.010158 1.183422 -0.002726

2365.78032388.59493036.6849

62.174276.711246.8783

P 1.535719 -0.162292 0.000000

H 1.345918 -1.135158 1.027683

H 1.345918 -1.135158 -1.027683

O 0.000000 0.541274 0.000000

O -2.226302 0.338121 0.000000

C -1.155577 -0.177300 0.000000

3c

H -0.983738 -1.266666 0.000000

74.7345128.0608263.677512.6377850.4533916.6315975.49881036.79871096.01071131.70571405.4991847.20942331.46422340.83892961.6911

2.79074.42961.266526.7263109.284714.26348.03051.0314

443.697922.25081.0497

372.927662.431599.802743.7388

P -1.451960 -0.378561 0.000000

H -2.086112 0.365550 1.030279

H -2.086112 0.365550 -1.030279

O 0.000000 0.507925 0.000000

O 2.228880 0.392587 0.000000

C 1.178286 -0.165926 0.000000

Formic phosphinous

anhydride (HCOOPH2)

3d

H 1.050872 -1.261216 0.000000

120.7747162.6008268.3894513.6433854.7161893.1981905.38911043.51261134.99991167.62151408.33061845.11412381.60032386.08992963.2315

0.623617.43890.882

29.4408137.781745.70979.20510.014963.1547290.54260.2279

425.780256.983469.463844.7596

11

Table S3: Computed cartesian coordinates (Å), vibrational frequencies (cm1), and IR intensities

(km mol1) for the species related to the decomposition of phosphino formic acid (H2PCOOH)

and carbamic acid (H2NCOOH).

Cartesian coordinateaName and notation Structure

Atom X Y ZVibrational frequency IR intensities

C -0.530773 0.162411 0.016685

O -1.091209 1.213331 -0.000882

P 1.322176 -0.076747 -0.11635

H 1.680347 1.132693 0.523835

H 1.445164 -0.89945 1.028789

O -1.211627 -1.042122 0.10817

P-Transition state1

H -1.350821 -1.426181 -0.765799

-558.4678181.9724294.7046424.9858504.5199728.1703804.6748819.42811045.23971110.28561136.91571815.38952415.84712430.48583798.7751

98.21949.08823.03620.755533.400217.527749.178121.7518

370.844617.147244.4199

273.972424.239837.1698

106.6803

C 0.000000 0.808781 0.000000

O -0.851089 1.631209 0.000000

P -0.195740 -1.289085 0.000000

H -0.813159 -1.933078 1.092627

H -0.813159 -1.933078 -1.092627

O 1.263982 0.742500 0.000000

P-Transition state 2

H 1.259269 -0.639924 0.000000

-1569.8479108.5644214.0492386.9166461.8801683.5734699.4035748.107

1043.12991057.09181220.35831756.58621974.53462429.6462466.066

750.8080.359388.53582.928154.8904

316.62293.254189.04360.307519.0705

364.6987128.8586454.046311.159316.7332

C -1.758337 -0.021397 -0.000069

O -1.657277 -1.177549 -0.000005

19.309530.516638.758580.2335

0.5220.75350.03613.4449

12

P 2.029748 0.046623 -0.000703

H 2.689860 -0.642734 1.050804

H 2.696063 -0.682919 -1.020710

O -1.874149 1.132979 -0.000070

PH3 and CO2 complex

H 2.969279 1.111242 -0.018542

98.6953663.5305672.65491017.54231136.75681137.17951371.51252392.01792399.43692401.79812416.2312

1.614652.100327.762926.86499.0569.98650.036638.098213.029456.9558

606.2279

P 0.000000 0.000000 0.128193

H 0.000000 1.194495 -0.640964

H 1.034463 -0.597247 -0.640964

Phosphine(PH3)

H -1.034463 -0.597247 -0.640964

1017.27721137.57261137.57262386.28492394.36142394.3618

19.876711.086311.086834.831167.42767.4207

C 0.000000 0.000000 0.000000

O 0.000000 0.000000 1.160338Carbon dioxide(CO2)

O 0.000000 0.000000 -1.160338

671.7935671.79351371.80792417.0441

31.862231.8622

0629.3311

C -0.037006 0.125500 -0.001350

O -0.449442 1.261103 0.004017

H 1.958089 0.470159 0.086017

H 1.524724 -1.207238 0.099975

O -0.848331 -0.968827 0.001643

Carbamic acid a

H -1.750996 -0.626480 0.004210

199.1585471.9527494.1470579.9022588.5957784.2446951.07801080.32331230.36281425.46101617.45361830.65903617.42673748.20963794.5707

218.958838.918422.304952.143443.955328.264345.430460.3494

186.9924126.8979107.6253506.788648.934159.844583.0179

13

N 1.267485 -0.246806 -0.032483

C 0.051288 -0.152712 0.001517

O 0.265864 -1.332549 0.007134

H -1.954612 -0.249845 0.059222

H -1.364511 1.307747 0.366927

O 1.072005 0.749392 0.021832

H 0.758864 1.633417 -0.199189

Carbamic acid b

N -1.207203 0.412886 -0.066827

341.3114440.4958517.3185556.0152610.8336775.2903936.95621083.30641235.91491359.72921638.49671859.71883569.55663679.49773804.8842

64.4970151.876014.6075

120.195717.623928.649847.327412.441441.0776

395.884263.9309

425.701225.668531.689940.2748

C 0.007256 0.159628 -0.006990

O 0.033637 1.358766 0.005407

H -2.001208 -0.126241 -0.041248

H -1.073440 -1.566425 -0.228230

O 1.151580 -0.619711 -0.107128

H 1.398185 -0.953734 0.762022

N-Transition state 1

N -1.121258 -0.603401 0.051881

-464.7408413.8169497.0835567.9784611.2456718.5407909.05291115.62881184.00091325.33911617.25581841.7922

35923718.09343818.2022

91.6562230.8078

1.813224.101110.335334.955272.430621.5935

121.6527217.19687.7414

467.468935.943344.424481.0914

C -0.311573 0.025927 -0.000002

O -1.290886 -0.647867 -0.000001

N-Transition state 2

H 1.411533 -1.070720 0.828749

-1731.7936331.8869451.5007592.2783767.8410785.0494983.01111037.74691277.3258

997.51406.072715.65132.1347

346.576910.598251.73025.1090

338.6580

14

H 1.411567 -1.070634 -0.828789

O -0.007706 1.269736 0.000001

H 1.166923 0.738544 0.000035

N 1.181165 -0.532529 0.000003

1387.29001565.91551891.18942151.68663480.88333579.7292

48.464264.1295

638.71906.296817.662633.8990

C 0.943817 -0.000377 0.000203

O 0.977312 1.159826 0.000085

H -2.402003 0.487207 0.800660

H -2.389209 0.453268 -0.824981

O 0.973082 -1.160753 0.000078

H -2.384439 -0.941262 0.017230

NH3 and CO2 complex

N -2.012914 0.001495 0.000653

13.626162.9738100.0007158.6617205.0578643.7116677.18511066.55841369.58371671.88211672.69702413.59643465.79423582.46343584.9789

0.146615.27750.840045.533922.052366.412731.6321

132.54591.029618.168318.7915

599.60380.52132.76413.2717

N 0.000000 0.000000 0.115439

H 0.000000 0.937566 -0.269357

H 0.811956 -0.468783 -0.269357

Ammonia (NH3)

H -0.811956 -0.468783 -0.269357

1063.24931676.18021676.18063465.04033581.54983581.5501

147.497616.912016.91202.36350.56750.5673

15

Table S4: Computed energies for various isomers of phosphino formic acid (H2PCOOH).

Species #B3LYP/cc-pVTZa

(CCSD/cc-pVTZa')

Ezpc b

(Ezpc b')

CCSD(T)/CBSc

(CCSD(T)/CBSc')

IE(eV)d

(IE(eV)d')

E(eV)e

(E(eV)e')

1a-531.779440

(-530.925802)

0.041665

(0.042656 )

-531.120540

(-531.120665)

9.75

(9.74)

0.00

(0.00) Phosphino formic

acid (H2PCOOH)1b

-531.771748

(-530.917714)

0.041360

(0.042377)

-531.112984

(-531.113136)

9.74

(9.73)

0.20

(0.20)

2a-531.746462

(-530.893148)

0.044725

(0.045718)

-531.092480

(-531.092602)

8.42

(8.43)

0.85

(0.85)

2b-531.746414

(-530.89293)

0.044291

(0.045314)

-531.091851

(-531.091976)

8.30

(8.31)

0.85

(0.85)

2c-531.746576

(-530.893015)

0.044273

(0.045308)

-531.091733

(-531.091869)

8.29

(8.29)

0.85

(0.86)

Enol tautomer

(HPC(OH)2)

2d-531.737190

(-530.883906)

0.043692

(0.044795)

-531.082305

(-531.082462)

8.23

(8.23)

1.10

(1.10)

3a-531.779510

(-530.926132)

0.041387

(0.042607)

-531.120326

(-531.120653)

9.50

(9.50)

0.00

(0.00)

3b-531.779167

(-530.925199)

0.041524

(0.042659)

-531.119587

(-531.119886)

9.48

(9.48)

0.02

(0.02)

3c-531.774531

(-530.920602)

0.040717

(0.041968)

-531.114341

(-531.114653)

9.36

(9.36)

0.14

(0.14)

Formic phosphinous

anhydride

(HCOOPH2)

3d-531.774417

(-530.920203)

0.041119

(0.042249)

-531.114272

(-531.114534)

9.34

(9.34)

0.16

(0.16) a B3LYP/cc-pVTZ energy with zero-point energy correction in hartree.a' CCSD/cc-pVTZ energy with zero-point energy correction in hartree.b B3LYP/cc-pVTZ zero-point energy in hartree.b' CCSD/cc-pVTZ zero-point energy in hartree.c CCSD(T)/CBS energy in hartree (B3LYP/cc-pVTZ optimized geometry).c' CCSD(T)/CBS energy in hartree (CCSD/cc-pVTZ optimized geometry).d CCSD(T)/CBS ionization energy in eV with B3LYP/cc-pVTZ zero-point energy correction.d' CCSD(T)/CBS ionization energy in eV with CCSD/cc-pVTZ zero-point energy correction.e CCSD(T)/CBS relative energy in eV with B3LYP/cc-pVTZ zero-point energy correction.e' CCSD(T)/CBS relative energy in eV with CCSD/cc-pVTZ zero-point energy correction.

16

Table S5: Computed energies for the species related to the decomposition of phosphino formic

acid (H2PCOOH) and carbamic acid (H2NCOOH).

SpeciesB3LYP/cc-pVTZa

(CCSD/cc-pVTZa')

Ezpc b

(Ezpc b')

CCSD(T)/CBSc

(CCSD(T)/CBSc')

E(kJ/mol)d

(E(kJ/mol)d')

Phosphino formic acid 1a-531.779440

(-530.925802)

0.041665

(0.042656 )

-531.120540

(-531.120665)

51

(52)

Phosphino formic acid 1b-531.771748

(-530.917714)

0.041360

(0.042377)

-531.112984

(-531.113136)

70

(71)

P-Transition state1-531.762122

(-530.908825)

0.039894

(0.040945)

-531.102259

(-531.102381)

94

(95)

P-Transition state2-531.707262

(-530.839762)

0.034742

(0.035725)

-531.035257

(-531.036070)

256

(256)

PH3 and CO2 complex-531.805267

(-530.949533)

0.036169

(0.036709)

-531.135784

(-531.135945)

-4

(-4)

PH3 + CO2-531.804993

(-530.948404)

0.035540

(0.036078)

-531.133704

(-531.133733)

0

(0)

Carbamic acid a -245.193124 0.051062 -244.922591 10

Carbamic acid b -245.181773 0.051052 -244.911794 38

N-Transition state 1 -245.177693 0.04996 -244.906250 50

N-Transition state 2 -245.128455 0.046209 -244.850349 187

NH3 and CO2 complex -245.202530 0.047132 -244.926008 -10

NH3 + CO2 -245.199329 0.045965 -244.921192 0 a B3LYP/cc-pVTZ energy with zero-point energy correction in hartree.a' CCSD/cc-pVTZ energy with zero-point energy correction in hartree.b B3LYP/cc-pVTZ zero-point energy in hartree.b' CCSD/cc-pVTZ zero-point energy in hartree.c CCSD(T)/CBS energy in hartree (B3LYP/cc-pVTZ optimized geometry).c' CCSD(T)/CBS energy in hartree (CCSD/cc-pVTZ optimized geometry).d CCSD(T)/CBS relative energy in kJ/mol with B3LYP/cc-pVTZ zero-point energy correction.d' CCSD(T)/CBS relative energy in kJ/mol with CCSD/cc-pVTZ zero-point energy correction.

17

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